THANKS dmtry for this long explanation !

> what happen if for exemple we increase the width of
> one varchar column during the backup ?
>bad question.

:(

>So, it's like snapshot that you make in time.
>For example, Level 0 - each month, level 1 - each week, and level 2 -
>each day.

yes i understand, but with level 2 each days, it's mean that if i m on
days 4 from the
level 1 the nbackup will backup the change from the last 4 days .. it's
mean more bigger
backup file, more IO ... and this when we know that i have already
backup the change of des 3 previous days :(

On 12/26/2011 1:45 AM, Dmitry Kuzmenko wrote:
>
> Hello, Vander!
>
> Sunday, December 25, 2011, 10:57:32 PM, you wrote:
>
> VCS> for exemple i see that during the backup, the database file is locked
> VCS> and all write are done in a separate delta file ... is this can slow
> VCS> down the server ?
> VCS> especially when the separate file is merge back with
> VCS> the database file ?
> Sure, because while writes goes to delta is ok, copying or scanning
> database for nbackup levels produces additional IO.
>
> VCS> what happen if for exemple we increase the width of
> VCS> one varchar column during the backup ?
> bad question.
>
> VCS> also i not understand the level strategy, in the doc they say we
> will
> VCS> rarelly go beyong level 3 or 4 but me what i want to do is to
> save on a
> VCS> daily basis ... so for me it's will be 30 levels min (because every
> VCS> month i will reset)... what wrong in this ?
>
> 30 levels is nonsense. Also I doubt that nbackup can handle
> command line with 30 files specified.
> Level 0 - full copy of DB.
> Level 1 - only pages that was changed from level 0
> Level 2 - only pages that was changed from level 1
> etc.
>
> So, it's like snapshot that you make in time.
> For example, Level 0 - each month, level 1 - each week, and level 2 -
> each day.
> Thus with only 3 levels (from 0 to 2) you can restore copy of the
> database for each day. Levels goes this way:
> 0
> -1
> --2 - pages that changed from level 1
> -1 - again, only pages changed from making level 0
> --2 - only pages changed from level 1
>
> So, you can combine some level 2 only with level 1 made before it, not
> after, of course.
> Creating such "a ladder" with 30 levels doesn't make any sense,
> because on restore database can be combined with levels down from
> highest, i.e. 2+1+0 in that example.
> As you plan to make each day 1 level plus, you will need for example
> at 15-th day to specify all 15 levels you made. Instead,
> you can make level 1 backup each day, and then use level 0+1 to
> restore database for particular day starting from the current month.
>
> Depending of the application activity, each level will have different
> size. It is hard to predict level sizes, because applications can
> rewrite same data, or different data.
>
> So, here is IO also. Using 30 levels needs to apply them all, one by
> one to the level 0 backup.
>
> And, remember, that nbackup makes physical copy of the database,
> page by page, and it is not interested about data or transaction
> numbers, etc.
>
> You can make level 0 copy of the database if you just stop the
> Firebird and copy database to another file.
>
> VCS> and to finish how nbackup can know what was changed from the last
> backup
> VCS> ?
>
> see above.
>
> VCS> does it's mean that every page in the database file have a version
> VCS> number ?
>
> It starts to have marks after each level of nbackup you make.
> That is how nbackup understands what pages was changed from the
> last nbackup level made.
>
> --
> Dmitry Kuzmenko, www.ib-aid.com
>
>


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